The present invention relates in general to spin-on filters which are designed to threadedly assemble to a mounting head and which include an annular face gasket. More specifically the present invention relates to the design of a floating retainer for the support and positioning of the annular face gasket relative to the nutplate and outer shell.
Spin-on fluid filters which are designed to threadedly assemble onto a mounting head of an engine typically include an outer shell, nutplate, filter cartridge, and annular face gasket. The connection or assembly of the outer shell to the nutplate is normally achieved by creating a sealed interface in one of two ways. A first method or way involves the creation of an annular interlocking seam between the metal of the shell and the metal of the nutplate. In this approach, adhesive may be applied between the formed and interlocking metal edges or lips of the two members to improve the security or integrity of the interlocking seam. A corollary to this method is to use a retainer for the gasket and interlock the outer peripheral edge of the retainer with the edge (metal) of the outer shell. In this approach, the nutplate is then captured by some other arrangement.
The second method or way involves forming the free peripheral edge of the outer shell around and over the outer peripheral edge of the nutplate. This "seamless" approach is intended to both capture the nutplate and provide a sealed interface between the nutplate and the outer shell. Since the internal pressure which must be handled by the fluid filter can reach relatively high levels, the mechanical connection between the outer shell and the nutplate will not always be sufficient to provide a secure seal. In this regard, a "secure" seal is one which is liquid-tight. As a means of preventing leakage from within the filter and through the interface between the outer shell and the nutplate, an annular gasket is typically used.
In U.S. Pat. No. 4,969,994 which issued Nov. 13, 1990 to Misgen et al., the outer shell is attached to the nutplate (see FIG. 3 of this patent) and an annular groove is formed in the nutplate for receipt of the annular gasket (item 134). The Misgen et al. patent also discloses a rollover seam design which is identified as "prior art" in FIG. 1 of the '994 patent. The rollover seam is created between the shell and the retainer or plate (12) and the retainer is shaped with a groove for receipt of the face gasket. In both styles disclosed in the Misgen et al. patent, FIGS. 1 and 3, the annular groove for receiving the annular face seal is fixed in size and position, causing a fairly precise shaping and sizing requirement for the gasket, which is to be received and retained in the groove.
While the two methods or approaches which have been described for connecting the outer shell and the nutplate (or retainer) for assembly of an annular gasket are regarded as typical, there are a number of related design considerations. For example, the metal thickness of the shell is one consideration, noting that if the thickness is increased, the interlocking seam with a nutplate or retainer has less risk of fluid bleeding therethrough. Since the interior of the filter will see high pressure and certain peak pressures, if a heavier or thicker metal is used for the outer shell, then when that metal is formed into an interlocking seam in combination with the metal of either the nutplate or the retainer, it is a more secure interface with less chance of leakage. There is of course a cost trade off when going to a thicker walled shell. The thickness of the nutplate is also a related design consideration. Since nutplates of the type used in fluid filters are typically metal stampings, there are certain limitations on the thickness and this is particularly significant when the gasket groove is to be formed in the nutplate. With a thicker nutplate there is less deflection under high pressure and with less deflection of the nutplate there is less risk of leakage. Ideally, a thicker nutplate will be used in order to withstand the higher static burst pressures, but the trade off is the difficulty or inability of forming (i.e., stamping) the required shapes and contours in the nutplate when the nutplate is used to create the annular groove for receipt of the face gasket.
When the groove for the annular face gasket is fixed in size and position, which is typical of existing and earlier designs, this forces a more precise sizing and shaping of the gasket. This design constraint creates a risk that the gasket will not properly seat in the groove and will not have the necessary compression fit and compression characteristics to establish the necessary and desired seal.
In designs which use some type of retainer to help capture the gasket, securing of the retainer to the nutplate becomes a consideration. If this approach is selected in order fix the position of the receiving groove, the retainer could be spot welded to the nutplate, but this presents a challenge due to the placement locations for the welding electrodes. There is also a limitation as to the sequence of steps. With a seamless (roll over) design, the retainer is located where it would interfere with the roller mechanism that is used to roll over the shell material around and over the peripheral edge of the nutplate. Accordingly, the retainer must be spot welded after the roll over operation is completed and this further complicates the welding procedure because it is difficult to place the welding electrodes on both sides of the nutplate and retainer combination after the nutplate has been joined to the outer shell.
After consideration of these various limitations, problems, and drawbacks with current filter designs, it will be appreciated that the present invention provides a number of improvements and advantages. The present invention uses a floating retainer which is thus able to be self-centering. The retainer captures the inside diameter of the face gasket and the rolled lip or inner peripheral wall portion of the shell captures the outside diameter of the gasket as that lip of the shell is rolled over the upper and outer peripheral edge of the nutplate. There is a side-to-side compression fit between the gasket and the retainer and between the gasket and the shell and this compression fit of the gasket helps to hold the retainer and gasket in the filter assembly until the filter assembly is threadedly assembled onto the mounting head.